This invention relates generally to conveyor sortation systems, or sorters, and, in particular, diverters used in such sortation systems. The invention is especially useful with sortation systems that, at least initially, divert articles without imparting a rotational motion on the article, also known as a parallel sorter. However, the invention is capable of other applications.
Various forms of conveyor sortation systems have been known, such as paddle diverters, pushers, pop-up chain and belt transfer assemblies, and the like. One particular advantageous form of a sortation system is a positive displacement sortation system in which a series of pusher shoes are mounted to travel in the direction of the conveying surface and, when diverted, to travel laterally along the conveying system to divert articles on the conveying surface. For example, articles may be diverted to takeaway conveyors, or spurs, arranged either on one side of the conveying surface, thereby defining a unilateral divert, or on both sides of the conveying surface, thereby defining a bilateral divert. The pusher shoes are propelled laterally by a propelling member extending below the conveying surface and selectively engaging a diverter rail which extends diagonally under the conveying surface. Diverters associated with the diverting rail selectively divert the propelling member onto the associated diverting rail in order to cause the pusher shoes to travel laterally of the conveying surface. If a particular pusher shoe is not diverted onto a particular diverting rail, then the shoe continues to travel solely in the direction of the conveying surface unless a downstream diverter diverts the pusher shoe onto its associated diverter rail. Examples of such positive displacement sorters are disclosed in commonly assigned U.S. Pat. Nos. 4,738,347 and 5,127,510, the disclosures of which are hereby incorporated herein by reference. Other examples of positive displacement sorters are disclosed in U.S. Pat. Nos. 3,361,247 and 4,884,677.
One form of a diverter is disclosed in U.S. Pat. No. 5,409,095, the disclosure of which is hereby incorporated herein by reference. The '095 patent discloses a diverter made up of an electromagnet that, when energized, attracts the propelling assembly of the pusher shoe and guides the propelling assembly onto the associated diverting rail. In the embodiment illustrated in the '095 patent, the propelling member includes a bearing made of a ferromagnetic, or magnetically permeable, substance, such as iron alloy. The electromagnet, when energized, attracts the bearing thereby diverting the associated pusher shoe onto the diverting rail associated with the diverter. The electromagnetic diverter disclosed in the '095 patent is desirable because it is capable of diverting pusher shoes traveling at a high rate of speed thereby increasing the throughput of articles sorted by the sorter. Additionally, the pusher shoes can be diverted with less noise than is produced with mechanical or electromechanical diverters.
Another form of diverter is a parallel divert sorter which, at least initially, diverts articles without rotating the articles. Such a parallel divert sorter is disclosed in commonly assigned U.S. Pat. Nos. 5,165,515; 5,927,465; 6,041,909; and 6,513,642 B1, the disclosures of which are hereby incorporated herein by reference. Because the articles are at least initially diverted without rotating the articles, it is possible to include a smaller gap between articles because it is not necessary to leave a sufficient gap for rotation of the articles. This also improves the throughput of the sorter. One difficulty of using an electromagnetic diverter with a parallel divert sorter is that it may be necessary to space the diverting rails and diverters as close together as the pitch between the pusher shoes. Because pusher shoe pitch may be as low as 5 or 6 inches, it may be necessary to utilize as low as 5-inch or 6-inch spacing between magnetic diverters. Because of the magnitude of the electromagnetic force necessary to attract the bearing of a pusher shoe in order to divert that pusher shoe onto a diverting rail, the size of the electromagnetic diverter becomes impractical for use in a parallel divert sorter of the type disclosed in the '515, '465, '909 and '642 patents.